U.S. patent number 5,685,758 [Application Number 08/631,390] was granted by the patent office on 1997-11-11 for hot melt adhesive compositions with improved wicking properties.
This patent grant is currently assigned to National Starch and Chemical Investment Holding Corporation. Invention is credited to Charles W. Paul, Gary Raykovitz, Matthew L. Sharak, Quinn Tong, Lydia Wagner, Bing Wu.
United States Patent |
5,685,758 |
Paul , et al. |
November 11, 1997 |
Hot melt adhesive compositions with improved wicking properties
Abstract
A nonwoven disposable article is constructed using adhesive
compositions containing 1 to 25% of a surfactant, which causes the
adhesive composition to exhibit a contact angle of 90.degree. or
less and a reduction in surface tension of less than or equal to
about 35-40 dynes/cm, giving improved wicking capabilities to the
nonwoven.
Inventors: |
Paul; Charles W. (Madison,
NJ), Sharak; Matthew L. (Franklin Park, NJ), Wu; Bing
(Somerville, NJ), Wagner; Lydia (Bedminster, NJ), Tong;
Quinn (Belle Mead, NJ), Raykovitz; Gary (Flemington,
NJ) |
Assignee: |
National Starch and Chemical
Investment Holding Corporation (Wilmington, DE)
|
Family
ID: |
24530993 |
Appl.
No.: |
08/631,390 |
Filed: |
April 12, 1996 |
Current U.S.
Class: |
442/409;
428/355EN; 442/411; 442/414 |
Current CPC
Class: |
A61L
15/34 (20130101); A61L 15/48 (20130101); A61L
15/42 (20130101); A61L 15/58 (20130101); Y10T
442/692 (20150401); Y10T 428/2878 (20150115); Y02P
20/141 (20151101); Y10T 442/696 (20150401); Y10T
442/69 (20150401) |
Current International
Class: |
A61L
15/58 (20060101); A61L 15/48 (20060101); A61L
15/16 (20060101); A61F 013/15 () |
Field of
Search: |
;428/355,261,355EN
;442/409,411,414 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Davis; Jenna
Attorney, Agent or Firm: Gennaro; Jane E.
Claims
We claim:
1. A disposable article containing an absorbent core bound together
or reinforced with hot melt adhesive fibers consisting of (a) 10 to
80 weight percent of an olefin containing polymer, (b) 10 to 70
weight percent of a compatible tackifying resin, c) 0 to 20%
plasticizer, (d) 0 to 2% stabilizer, (e) 0 to 25% wax, and (f) 1 to
25% of a surfactant, which surfactant will cause the adhesive
composition to exhibit a contact angle of 90.degree. or less and a
reduction in surface tension of less than about 40 dynes/cm.
2. The disposable article according to claim 1 in which the
surfactant is an ethoxylate of C.sub.1 -C.sub.18 alkyl or dialkyl
phenol; an ethoxylate of an alkyl C.sub.8 -C.sub.60 mono-alcohol;
an ethylene oxide/propylene oxide block copolymer having a Mn of
200 to 3000; a benzoate formed by partial condensation of benzoic
acid with a hydrophilic di- or mono-ol having less than 1000 Mn; a
C.sub.8 -C.sub.60 alkyl ethoxylate sulfonate; an alkyl C.sub.8
-C.sub.60 sulfonate; an alkyl/aromatic sulfonate; or an ethoxylate
or propoxylate of polydimethyl siloxane having a number average
molecular weight of 500 to 10,000.
3. The disposable article according to claim 1 in which the
surfactant is a crystallizable surfactant.
4. The disposable article according to claim 1 in which the olefin
containing polymer is present in an amount of 40 to 60 weight
percent.
5. The disposable article according to claim 1 in which the
tackifying resin is present in an amount of 30 to 60 weight
percent.
Description
FIELD OF THE INVENTION
This invention relates to hot melt adhesives for bonding nonwoven
fabrics and tissues.
BACKGROUND OF THE INVENTION
A nonwoven fabric is an interlocking network of synthetic or
naturally occurring fibers, or a combination of the two, in which
the individual fibers are mechanically, chemically, or thermally
bonded to each other. Tissue is a closely related material in which
the individual fibers may or may not be bonded to one another. The
fabric or tissue is characterized by flexibility, porosity and
integrity. Nonwovens are used commercially for a variety of
applications including insulation, packaging, household wipes,
surgical drapes, medical dressings, and disposable articles, such
as, diapers, adult incontinent products and sanitary napkins.
In many of the end use applications it is necessary to adhere the
nonwoven or tissue to another substrate or component. The second
substrate may be another nonwoven, tissue, or an unrelated
material, such as a polyethylene film. Commonly, hot melt adhesives
are employed to bond the assembly together. Hot melt adhesives
allow for cost and time efficient manufacturing since there is no
evaporation step necessary as is the case for water based or
solvent based adhesive systems. For nonwoven applications, suitable
hot melt adhesives must possess good flexibility (or hand); no
staining or bleed through; suitable viscosity, set speed and open
time to function on commercially available equipment; and finally,
acceptable thermal aging properties.
Another desired property for hot melt adhesives, especially
important in disposable diaper, sanitary napkin, and bed pad
constructions, is the ability of the hot melt adhesive to transmit
liquid or moisture from the nonwoven fibers into the superabsorbent
or fluff core substrates. This property, referred to as strike
through, is desirable to draw the moisture away from the body and
into the absorbent core as quickly as possible after the nonwoven
is wetted.
Many hot melt adhesives are hydrophobic and repel moisture, rather
than drawing it through the adhesive and into the absorbent core.
It is known to use fluorchemical surfactants in some hot melt
adhesives to provide improved strike through without reducing the
absorbency speed or capacity of the absorbing material. In addition
to their use as construction adhesives, hot melt adhesives may be
used to bind or reinforce the nonwoven fibers together. These hot
melts adhesives may also be formulated to provide improved strike
through by fluorosurfactants. However, fluorosurfactants are
costly, absorb through the skin, and persist in the body. These
limitations make them unsuitable for disposable nonwovens that are
in direct contact with the body.
SUMMARY OF THE INVENTION
We have discovered that, when used at the proper level, the
addition of a variety of hydrocarbon and silicone surfactants to
conventional olefin-containing hot melts for use in nonwovens
confers the unexpected benefits of improved fluid acquisition rates
and spreading (wicking), and resistance to high humidity and direct
water immersion.
This invention is a disposable article containing at least one
nonwoven or tissue layer bonded to another nonwoven, tissue, or
polyolefin film layer using a hot melt adhesive composition
consisting of (a) 10 to 80 weight percent, preferred 40 to 60
weight percent, of an olefin containing polymer, (b) 10 to 70
weight percent, preferred 30 to 60 weight percent of a compatible
tackifying resin, c) 0 to 20% plasticizer, (d) 0 to 2% stabilizer,
(e) 0 to 25% wax, and (f) 1-25% of a surfactant, which surfactant
will cause the adhesive composition to exhibit a contact angle of
90.degree. or less and a reduction in surface tension of less than
about 35-40 dynes/cm, preferably less than or equal to 35 dynes/cm,
preferably 30 dynes/cm, more preferably 20 dynes/cm.
When a droplet of liquid is placed on a uniform, perfectly flat,
solid surface, its shape and the length of time that it holds its
shape are determined by three interfacial tension forces: the force
of the solid surface, the surface tension of the liquid, and the
force at the solid/liquid interface. The angle that the tangent
(edge) of the liquid droplet makes with the solid surface is a
measured value relative to those combined vector forces. In
general, the smaller the contact angle, .THETA., the greater the
tendency of the liquid droplet to lose its shape and spread. The
addition of surfactants to the liquid causes a reduction of surface
tension of the droplet.
In the case of hot melt adhesives for use in the construction of
nonwoven applications, the addition of surfactant to the adhesive
causes a decrease in the contact angle, .THETA., of any fluid
against the adhesive. As a result the presence of the surfactant
makes the adhesive more effective in transmitting fluids through
the adhesive layer and into the core of the superabsorbent
material. The same result would be obtained if the surfactant were
added to a hot melt adhesive used for binding or reinforcing the
nonwoven fibers. At the same time that the contact angle of the
fluid is reduced, the surface tension is also reduced, but this
lessens the capability of the fluid to wick through to the core of
the nonwoven. Thus, in preparing the adhesives for this
application, a balance must be achieved in the type and amount of
surfactant used to provide the optimum performance. It has been
found that optimum performance is obtained by the addition of a
surfactant to the hot melt adhesives of a type and in an amount so
that the fluid passing through the disposable exhibits a contact
angle of less than 90.degree., and a reduction in surface tension
of less than about 35-40 dynes/cm, preferably less than or equal to
35 dynes/cm.
The improved hot melt adhesive composition used in the disposable
articles of this invention helps prevent leakage from the absorbent
core and allows the use of thinner absorbent core substrates.
The preferred surfactants are ethoxylates of mono-alcohols and are
present in the adhesive in an amount from 1 to 25 weight percent.
Ethoxylates of mono-alcohols are the reaction products of the
polymerization of ethylene oxide initiated at the --OH site of the
alcohol.
The addition of the surfactant increases the hydrophilic character
of the hot melt adhesive and improves its strike through properties
rather than causing it, as compared to conventional hot melts, to
act as a barrier to the liquid transmission.
DETAILED DESCRIPTION OF THE INVENTION
The surfactants utilized herein will be any of those surfactants,
which when added in sufficient amount to the adhesive composition
will impart improved wicking properties to the adhesive without
causing a loss in adhesive properties.
Particularly preferred are the higher crystalline type surfactants,
such as Unithox 480, a product of Petrolite Specialty Polymers
Group, Tulsa, Okla.
Typically, the surfactants will be used in amounts of 1 to 25%,
preferably 5 to 15% by weight, but the exact preferred range will
depend on the individual adhesive system.
Suitable surfactants include nonionic, anionic, and silicone
surfactants. Exemplary nonionic surfactants are:
ethoxylates of (i) C.sub.1 -C.sub.18, preferred C.sub.8 -C.sub.9
alkyl or dialkyl phenols, such as those sold under the tradenames
Macol DNP-10, available from PPG Industries, Gurnee, Ill., a 10
mole ethoxylate of dinonyl phenol, and Triton X-100, available from
Union Carbide, a 10 mole ethoxylate of octyl phenol; (ii) alkyl
C.sub.8 -C.sub.60 mono-alcohols, such as those sold under the
tradenames Surfonic L-12-8, an 8 mole ethoxylate of dodecanol,
available from Huntsman Chemical Co., and Unithox 480, a 38 mole
ethoxylate crystalline surfactant available from Petrolite
Specialty Polymers Group, Tulsa, Okla.; and (iii) propylene oxide
polymers, such as those sold under the tradename Pluronic, which
are ethylene oxide/propylene oxide block copolymers having a Mn of
200 to 3000 available from BASF; and
benzoates formed by partial condensation of benzoic acid with
hydrophilic di or mono-ols having less than 1000 Mn, such as the
product of condensing about three equivalents of benzoic acid with
four equivalent of diethylene glycol, commercially available as XP
1010 from Velsicol Chemical.
Suitable anionic surfactants are:
C.sub.8 -C.sub.60 alkyl ethoxylate sulfonates, (CH.sub.3
--(CH.sub.2).sub.11-14 --(O--CH.sub.2 CH.sub.2).sub.3 --SO.sub.3-
Na.sup.+, such as, Avenel S30, available from PPG Industries;
alkyl C.sub.8 -C.sub.60 sulfonates, such as, Rhodapon UB (C.sub.12
--SO.sub.3.sup.- Na.sup.+) available from Rhone Poulenc;
and alkyl/aromatic sulfonates, such as are represented by the
structure ##STR1## and sold under the tradename Calsoft.
Suitable silicone surfactants are ethoxylates or propoxylates of
polydimethyl siloxane, having a number average molecular weight of
500 to 10,000, preferably 600 to 6000, such as are sold under the
tradenames Silwet L-77, L-7605, and L-7500 available from OSi
Specialties, Danbury, Conn.; and product 193 from Dow Corning.
The preferred surfactants are those with lower molecular weights
because these have increased compatibility in the adhesive
formulations. The maximum acceptable molecular weight depends on
the type of surfactant and the other ingredients in the adhesive
formulation.
The surfactant may be added to any olefin-containing polymers
commonly used for disposable applications.
Suitable olefin-containing polymers are those in which ethylene is
polymerized with 15 to 45% by weight of copolymerizable monomers
such as vinyl acetate, N-butyl acrylate, propylene, methyl
acrylate, methyl acrylic acid, acrylic acid, metallocene catalyzed
ethylene based polymers and the like, as well as any mixtures
thereof.
Additional suitable polymers are pure homopolymers or copolymers of
the following monomers: olefins, such as ethylene, propylene,
butene, hexene octene, or other alpha-olefins; vinyl monomers, such
as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl
hexanoate; acrylic monomers, such as acrylic acid and methacrylic
acid, methacrylic acid esters, hydroxy ethyl acrylate, and the
like.
Preferred polymers are ethylene/vinyl acetate copolymers such as
those obtainable from Dupont under the Elvax tradename. The
preferred range for the vinyl acetate will be in the range of
18%-40% by weight, with 33% most preferred. Also preferred are
polyolefin polymers such as those obtainable under the Vestoplast
tradename from Huls.
Other adhesive compositions may be prepared according to the
invention using, as a base polymer, amorphous polyolefins or blends
thereof. Amorphous polyolefins are made by the atactic
polymerization of polypropylene. Polymerization occurs in the
presence of a catalyst comprising a coordination complex of a
transition metal halide with an organometallic compound. The solid
amorphous polypropylene has a softening point of about 150.degree.
C. and a Brookfield viscosity at 190.degree. C. of 1,000 to 50,000
cps. Suitable commercial products include Eastman Chemical's P
1010. Copolymers of amorphous polypropylene and ethylene (APE), or
butene (APB), or hexene (APH), are suitable as a base polymer, as
are terpolymers of propylene, butene and ethylene (APBE). Suitable
commercially available products include those sold under the
tradenames: Rextac 2315 from Rexene (APE); Rextac 2730 from Rexene
(APB); Vestoplast 750 and 708 from Huls (APBE).
Blends of any of the above base materials, such as blends of
ethylene vinyl acetate and atactic polypropylene may also be used
to prepare the hot melt adhesive compositions.
In all cases, the adhesives are formulated with tackifying resins,
plasticizers, waxes and/or other conventional additives in varying
amounts as are known to those skilled in the art.
The tackifying resins useful in the adhesive compositions can be
any compatible hydrocarbon resins, synthetic polyterpenes, rosin
esters, natural terpenes, and the like. More particularly, and
depending upon the particular base polymer, the useful tackifying
resins include (1) natural and modified rosins, for example, gum
rosin, wood rosin, tall oil rosin, distilled rosin, hydrogenated
rosin, dimerized rosin, and polymerized rosin; (2) glycerol and
pentaerythritol esters of natural and modified rosins, for example,
the glycerol ester of pale wood rosin, the glycerol ester of
hydrogenated rosin, the glycerol ester of polymerized rosin, the
pentaerythritol ester of hydrogenated rosin, and the
phenolic-modified pentaerythritol ester of rosin; (3) copolymers
and terpolymers of natural terpenes, for example, styrene/terpene
and alpha methyl styrene/terpene; (4) polyterpene resins having a
softening point, as determined by ASTM method E28-58T, of
80.degree. to 150.degree. C.; the latter polyterpene resins
generally resulting from the polymerization of terpene
hydrocarbons, such as the bicyclic monoterpene known as pinene, in
the presence of Friedel-Crafts catalysts at moderately low
temperatures; and hydrogenated polyterpene resins; (5) phenolic
modified terpene resins and hydrogenated derivatives thereof, for
example, the resin product resulting from the condensation, in an
acidic medium, of a bicyclic terpene and a phenol; (6) aliphatic
petroleum hydrocarbon resins having a Ball and Ring softening point
of 70.degree. to 135.degree. C.; the latter resins resulting from
the polymerization of monomers primarily consisting of olefins and
di-olefins; and the hydrogenated aliphatic petroleum hydrocarbon
resins; (7) aromatic petroleum hydrocarbon resins and the
hydrogenated derivatives thereof; (8) alicyclic petroleum
hydrocarbon resins and the hydrogenated derivatives thereof; and
(9) aromatic/aliphatic or alicyclic hydrocarbon resins, such as
those sold under the trademarks ECR 149B and ECR 179A by Exxon
Chemical Company. Mixtures of two or more of the above described
tackifying resins may be required for some formulations.
Various plasticizing or extending oils may also be present in the
composition in amounts of up to about 20%, preferably 0 to 15%, by
weight in order to provide wetting action and/or viscosity control.
The above broadly includes not only the usual plasticizing oils but
also use of olefin oligomers and low molecular weight polymers, as
well as vegetable and animal oils and their derivatives. Petroleum
derived oils that may be employed are relatively high boiling
materials containing only a minor proportion of aromatic
hydrocarbons (preferably less than 30% and, more particularly, less
than 15% by weight of the oil). Alternatively, the oil may be
totally non-aromatic. The oligomers may be polypropylenes,
polybutenes, hydrogenated polyisoprene, hydrogenated polybutadiene,
or the like, having average molecular weights between about 350 and
about 10,000. Vegetable and animal oils include glyceryl esters of
the usual fatty acids and polymerization products thereof.
Also useful as plasticizers are polar synthetic compounds, such as
the aliphatic and aromatic polyester plasticizers available from C.
P. Hall Co., Stow, Ohio. Amides phosphate esters, sulfonamides, and
phthalates are also suitable at varying levels.
Various petroleum derived waxes may also be used in amounts less
than about 25% by weight of the composition in order to impart
fluidity in the molten condition of the adhesive and flexibility to
the set adhesive, and to serve as a wetting agent for bonding
cellulosic fibers. The term "petroleum derived wax" includes both
paraffin and microcrystalline waxes having melting points within
the range of 130.degree. to 225.degree. F. as well as synthetic
waxes such as low molecular weight polyethylene or Fisher-Tropsch
waxes.
An antioxidant or stabilizer may also be included in the adhesive
compositions in amounts of up to about 3% by weight. Among the
applicable antioxidants or stabilizers are high molecular weight
hindered phenols and multifunctional phenols, such as sulfur and
phosphorous-containing phenols. Representative hindered phenols
include: 1,3,5-trimethyl 2,4,6-tris
(3,5-di-tert-butyl-4-hydroxy-benzyl)benzene; pentaerythritol
tetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate;
n-octadecyl-3,5-di-tert-butyl-4-hydroxyphenol)-propionate;
4,4'-methylenebis (2,6-tert-butylphenol); 4,4'-thiobis
(6-tert-butyl-o-cresol); 2,6-di-tertbutylphenol;
6-(4-hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1,3,5-triazine;
di-n-octadecyl 3,5-di-tert-butyl-4-hydroxybenzyl-phosphonate;
2-(n-octylthio)-ethyl 3,5-di-tert-butyl-4-hydroxy-benzoate; and
sorbitol
hexa[3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate].
Other additives conventionally used in hot melt adhesives to
satisfy different properties and meet specific application
requirements also may be added, and include fillers, pigments, flow
modifiers, dyestuffs, etc., which may be incorporated in minor or
larger amounts into the adhesive formulation, depending on the
purpose.
These hot melt adhesives may be prepared using techniques known in
the art. Typically, the adhesive compositions are prepared by
blending the components in the melt at a temperature of about
100.degree. to 200.degree. C. until a homogeneous blend is
obtained, approximately two hours. Various methods of blending are
known and any method that produces a homogeneous blend is
satisfactory. The resulting adhesives are characterized in that
they have a viscosity of 50,000 cP or less at the application
temperature of 350.degree. F. (177.degree. C.) or less. The
viscosity as used herein is a Brookfield viscosity measured using a
Brookfield viscometer model No. DV-II with spindle no. 27 at 10
rpm.
The resulting adhesives of the present invention are characterized
by their ability to provide a durable bond to a nonwoven or tissue
article and otherwise meet the unique requirements of the
application (including flexibility, non-staining, and machinable
viscosity). The adhesives described herein also possess exceptional
thermal stability, which distinguishes them from other moisture
sensitive technologies. Further, their hydrophilic natures
facilitate ready transmission of the fluid throughout the
construction.
The adhesive product can be applied to a substrate such as a
nonwoven article or tissue by a variety of methods including
coating or spraying in an amount sufficient to cause the article to
adhere to another substrate, such as tissue, nonwoven, or other
conventionally employed substrates, such as polyolefin films.
The following examples illustrate the compositions of suitable hot
melt adhesives, and the improvement to their wicking properties as
a result of the incorporation of the described surfactants.
EXAMPLES
Sample adhesives were prepared and tested for water contact angle,
surface tension reduction, and rate of wicking.
Raw Materials
The following raw materials were used:
Elvax 460, an ethylene/vinyl acetate (EVA) copolymer from DuPont
containing 18% vinyl acetate (VA), with a melt flow index (MFI) of
2.5 (dg/min at 190.degree. C. using a 2.2 kg weight) (the MFI for
the following are measured the same);
Elvax 265, an EVA from DuPont containing 28% VA, 3 MFI;
Elvax 200W, an EVA from DuPont containing 28% VA, 2500 MFI;
Elvax 140W, an EVA from DuPont containing 33% VA, 400 MFI;
Elvax 210W, an EVA from DuPont containing 28% VA, 400 MFI;
Elvax 40W, an EVA from DuPont containing 40% VA, 51 MFI;
Unitac 100 L, a rosin ester tackifier available from Union
Camp;
Macol DNP-10, a 10 mole ethoxylate of dinonyl phenol from PPG;
Nirez V2040 HM, a terpene phenolic tackifier available from Arizona
Chemical;
Zonatac 85L and 105L, styrenated terpenes with softening points at
85.degree. and 105.degree. C., respectively, from Arizona
Chemical;
Irganox 1010, a hindered phenol anti-oxidant available from
Ciba-Geigy;
Triton X-100, a 10 mole ethoxylate of octyl phenol available from
Union Carbide;
Surfonic DNP-100, a 10 mole ethoxylate of dinonyl phenol available
from Huntsman;
L12-8, an 8 mole ethoxylate of dodecanol available from
Huntsman;
Pycal 94, a 4 mole ethoxylate of phenol available from ICI;
Unithox 480, an ethoxylated C.sub.30 mono-ol with a molecular
weight of 2250 g/mole, available from Petrolite Specialty Polymers
Group, Tulsa, Okla.;
Escorez 2520, a liquid aliphatic/aromatic C.sub.5 -C.sub.9 resin
available from Exxon Chemical;
Nirez M85NS, an aromatic modified polyterpene available from
Arizona Chemical;
Nirez V2040HM, a terpene phenolic tackifier available from Arizona
Chemical;
Newtac 300, a phenol modified polyterpene available from Arizona
Chemical;
AC-400, an EVA wax with 13% VA and a viscosity at 140.degree. C. of
595 cP, available from Allied-Signal;
Macol DNP-10, a 10 mole ethoxylate of dinonyl phenol from PPG
Industries;
Avenel S30, an anionic surfactant, sodium sulfonated 3 mole
ethoxylate of a C.sub.12-15 mono-ol, available from PPG
industries;
Rhodapon UB, an anionic surfactant, sodium lauryl sulfate,
available from Rhone Poulenc;
Silwet L-77, L-7605 and L-7500, silicone surfactants available from
OSI Specialties;
Pluronic F38, F68, P65, P85, P61 and L44, ethylene oxide/propylene
oxide block copolymer surfactants available from BASF;
Unitac R98L, hydrogenated rosin ester available from Union Camp;
and
Jordapon CI, a prilled form of sodium cocoyl isethionate from PPG
Industries;
Aerosol MA80, a sodium hexyl sulfo-succinate from Cytec Industries;
and
Naugard HM22, an aromatic amine/hindered phenol blend available
from Uniroyal;
Eastotac, a dicyclopentadiene-based tackifier available from
Eastman Chemical Co.
Example I
Sample adhesive compositions for construction of nonwoven articles
were formulated from the above listed raw materials to the
following compositions in parts by weight (PBW). The adhesive used
as a control contained no surfactant.
______________________________________ PBW
______________________________________ Control Elvax 140W 45.0
Zonatac 85L 55.0 Irganox 1010 0.3 Sample A Elvax 200W 7.0 Elvax 40W
5.0 Elvax 140 W 34.5 Sylvatac 4100 19.0 Escorez 2520 5.0 AC-400 7.0
L12-8 10.0 Nirez M85NS 16.0 Sample B Elvax 200W 7.0 Elvax 40W 5.0
Elvax 140 W 34.5 Sylvatac 4100 19.0 Escorez 2520 5.0 AC-400 7.0
Surfonic DNP-100 10.0 Naugard HM22 0.3 Zonatac 85L 16.0 Sample C
Elvax 200 12.5 Elvax 140W 33.0 Escorez 2520 4.5 AC-400 6.0 Zonatac
85L 16.0 Irganox 1010 0.3 Macol DNP-10 10.0 Samples D-N Elvax 140W
50.0 Zonatac 105L 40.0 Irganox 1010 0.5 Surfactant 10.0 Sampes O-T
Elvax 140W 40.0 Zonatac 105L 50.0 Irganox 1010 0.5 Surfactant 10.0
______________________________________
The surfactant in each of the samples D-T was varied as reported
here by tradename:
______________________________________ Sample Surfactant Sample
Surfactant ______________________________________ D Triton X-100 E
Macol DNP10 F 193 Surfactant G Avanel S30 H Jordapon Cl I Rhodapon
UB J Aerosol MA8O K CalSoft L Silwet L-77 M Silwet L-7605 N Silwet
L-7500 O Pluronic F38, 80% EO, MW 4500 P Pluronic F68, 80% EO, MW
9000 Q Pluronic P65, 50% EO, MW 3600 R Pluronic P85, 50% EO, MW
4800 S Pluronic P61, 10% EO, MW 2000 T Pluronic L44, 40% EO, MW
2200 ______________________________________
The following procedures were used to test the samples.
Contact Angle Test
The contact angle is measured with the use of a goniometer, which
has a microsyringe for dispensing accurate droplet sizes and a
camera for photographing the angle of the liquid drop as it meets
the surface of the solid. The contact angle is measured as the
angle between The substrate and the tangent of the liquid drop (at
the interface). The lower the angle, the more effective the coating
is in transmitting (wicking) the liquid through the discontinuous
adhesive layer.
Surface Tension
The water surface tension was measured using the Dunuoy ring
method. Two grams of adhesive were placed in a clean 110 ml glass
jar with a 5 cm inner diameter, melted in a 135.degree. C. oven,
and then cooled to room temperature. Twenty ml of 0.85% saline
solution was added to the dish. The surface tensions of the pure
saline solution and of the saline solution after 15 minutes
exposure to the adhesive were measured using a KRUS K-14
tensiometer. The difference in the surface tensions were recorded
as the surface tension reduction (STR).
Fluid Wicking Area
Samples of substrate, 3 inches wide by 10 inches long, including
the adhesive coverage area, are taped to Plexiglass 3 inches from
the top on the front, and wrapped around to 3 inches from the top
on the back side. The samples are conditioned at 72.degree. F./50%
RH for 24 hours. A one liter beaker is filled to the 200 mL level,
with 0.9% saline solution dyed red. The sample is placed into the
beaker and the fluid is allowed to rise for 2 minutes, at which
time the sample is removed from the beaker and the total wicking
area is calculated (within 10 seconds).
The results of these tests are tabulated here and show that the
addition of the surfactant causes an increase in the surface
wicking area (samples C and E); causes the contact angle to be less
than 90.degree. (samples A-G, K, and M-T); and results in a surface
tension reduction of about 35 dynes/cm or less.
______________________________________ Contact Surface Tension
Fluid Wicking Sample Angle Reduction Area
______________________________________ Control 110-112.degree. 20.2
in.sup.2 A 61.degree. B <17.degree..sup. C <30.degree..sup.
21.5 in.sup.2 D <30.degree..sup. E <30.degree..sup. 28 21.2
in.sup.2 F 54 32 G 47 35 H 36 I 6 J 26 K 65 22 L 37 M 76 28 N 73 30
O 46 12 P 41 17 Q 42 26 R 39 24 S 49 26 T 54 22
______________________________________
Adhesive sample E was chosen as the representative sample for
comparison to the control adhesive in tests to measure bond
strength after exposure to humidity or to soaking in water. The
adhesives were tested according to the following test
procedures.
Humidity Test
Sample nonwoven fabrics were adhered or bonded to a polyethylene
substrate using the above adhesive compositions at a temperature of
149.degree. C. (300.degree. F.), applied by a coater machine at 450
ft/min. and 2.66 g/m.sup.2. Two sets of adhesive bonds were
prepared for each adhesive and conditioned for three days: one set
at ambient conditions, and the second at 49.degree. C. (120.degree.
F.), 90% RH. A rubber-based construction adhesive with no
surfactant was used as a control. After conditioning, the bonds
were pulled on an Instron machine at 12 in/min crosshead speed, 2
in/min chart speed in a 180.degree. T peel mode. The average peel
mode of four trials was recorded; if there was bond failure, the
type of failure was recorded instead of peel value.
Soak Test
Poly to nonwoven bonds were made on samples as described above, and
also with a rubber based adhesive containing 28 parts by weight of
styrene/isoprene/styrene, 56 parts by weight of a partially
saponified rosin, and 16 parts by weight of the surfactant sold
under the trademark Macol DNP-10. Bonds were made using the coater
machine at 300.degree. F., 450 ft/min. and 4.5.sup.9 /m.sup.2. For
each adhesive, one set of bonds was stored in ambient conditions. A
second set was soaked in room temperature deionized water for one
hour, after which the water was drained and the bonds immediately
tested. Bonds were pulled on the Instron machine at 12 in/min
crosshead speed, 2 in/min chart speed in a 180.degree. T peel mode.
The average peel mode of four trials was recorded; if there was
bond failure, the type of failure was recorded instead of peel
value.
The results of both tests are reported in the following Table.
______________________________________ Bond Strengths Rubber- based
adh. Control with Conditions Sample E adh. surfactant
______________________________________ Ambient 207 g 275 g 72 hrs.
120.degree. F. 182 g 331 g 90% R.H. Failure Mode 3 2 Ambient - dry
152 g 264 g 348 g Soaking - wet 189 g 292 g no bond Failure Mode -
dry 1 1 1 Failure Mode - wet 2 1 not testable
______________________________________
The code for the failure modes is the following:
1. Adhesive failure from nonwoven, with some fiber pullout.
2. Adhesive failure from nonwoven, no visible fiber pullout.
3. Adhesive failure from poly.
4. Cohesive failure mostly to poly.
The bond held with the rubber based adhesive with surfactant fell
apart during the soak test.
The samples conditioned by soaking may have greater bond strength
values than the samples conditioned in ambient temperature and
humidity due to softening of the adhesive or matting of the
nonwoven.
The results of this test show that excellent poly/non-woven bonds
can be obtained, which resist high humidity and direct water
immersion, despite their low contact angle.
Example II
Benefits of Crystalline Surfactants
This example used crystallizable surfactants to achieve low water
contact angle and low water STR. The crystallinity of the
surfactant significantly decreases the mobility of the surfactant
and thus results in low water STR. Depending on the molecular
structure, the crystalline site can be either the hydrophobic
portion or the hydrophilic portion of the surfactant, or both. The
improvement in water STR is shown in the table below. The
formulations give components in parts by weight in parentheses.
______________________________________ Crystalliz- ability of the
Contact STR Viscosity Formulation surfactant Angle (dynes/cm)
(135.degree. C.) ______________________________________ Example E
no <30 28 10,500 cps Example U yes (both <30 14 9,000 cps
Elvax 210W (40) hydrophilic Zonatac 105L (50) and Irganox 1010
(0.5) hydrophobic Unithox 480 (10) portions) Example V yes (both
<30 14 9,500 cps Elvax 140W (40) hydrophilic Zonatac 105L (50)
and Irganox 1010 (0.5) hydrophobic Unithox 480 (10) portions)
______________________________________
The crystallization of the surfactant in Examples U and V is
confirmed by DSC measurements performed with a Perkin-Elmer DSC-7.
The sample was heated to 150.degree. C., held for 5 minutes at that
temperature, and cooled to room temperature at 10.degree. C./min.
The sample was then reheated at 10.degree. C./min., and this run
was used to determine the crystallinity of the surfactant in the
formulation. The heat of fusion and melting point of the sample
were determined on the reheat cycle. By itself, Unithox 480
material exhibits a melting peak at 56.degree. C. and a heat of
fusion of 112 J/g. In the adhesive formulations U and V a melting
peak at 53.degree. C. is observed superimposed on that of the EVA
base polymers. This peak indicates that the surfactant is
recrystallizing in the formulations (thus, is crystallizable).
Example III
These are examples of high viscosity, high strength, faster setting
adhesives suitable for use as binder fibers when comingled with
other fibers in a nonwoven fabric. The compositions are given in
parts by weight in the following table in parts by weight, and the
identity of the raw materials can be found earlier in this
specification.
______________________________________ Adhesive Compositions AA BB
CC DD EE FF GG ______________________________________ Components
Elvax 460 50 50 50 50 50 Elvax 265 50 50 Unitac 100L 40 20 40
Zonatac 105L 40 40 Eastotac H100 20 Nirez V2040HM 20 20 40 DNP-10
10 10 10 10 10 10 10 Irganox 1010 0.5 0.5 0.5 Viscosity (P) at
200.degree. C. 975 1030 1045 1185 8870 945 910
______________________________________
For samples AA-DD, 100 g of each sample was held at 177.degree. C.
(350.degree. F.) in a glass jar for 24 hours. No phase separation
occurred for any sample. A solidified puddle of each adhesive
(about 5 cm in diameter by 1.5 mm thick) was held at 38.degree. C.
(100.degree. F./95% RH) overnight. No exudation of surfactant
occurred. A drop of water was place gently by pipette on the
surface of each adhesive. Adhesives BB-DD showed contact angles of
60.degree.-80.degree., which fell as the drop stood. Adhesive AA
gave almost instantaneous wet out of the water drop. On a larger
scale, 1000 lbs of adhesive AA was prepared in a sigma-blade mixer,
fed molten into an extruder, and pelletized underwater.
All three samples EE-GG were readily wet out by a drop of water.
The lower vinyl acetate content of adhesive EE makes it a harder
product compared to sample GG.
In summary, the results show that these adhesives may be
successfully used to form nonwoven disposable products. It will be
apparent that various changes and modifications may be made in the
embodiments of the invention described above, without departing
from the scope of the invention, as defined in the appended claims,
and it is intended therefore, that all matter contained in the
foregoing description shall be interpreted as illustrative only and
not limitative of the invention.
* * * * *